Transmission control protocol (TCP) utilizes a sequence number in a packet to identify the order and number of payload bytes communicated from one computer node to another so that data can be properly reconstructed, regardless of any fragmentation or packet loss that may occur during transmission. Notably, the sequence number is incremented to respectively represent each payload byte that has been previously transmitted by a sending node.
Replaying a capture file (e.g., a plurality of previously captured network packets that may be replayed to simulate a real world traffic environment/scenario) having TCP packets over Internet protocol (IP) (i.e. replay of an IP payload) does not require any special handling for TCP sequence or acknowledgment numbers unless the exact payload is to be replayed from a different originating host. Specifically, problems can arise when the payload is modified during replay to simulate a real world scenario. One exemplary scenario occurs when a sending peer node prepares to replay an HTTP capture file and the original host name (e.g., www.google.com) of a GET command needs to be modified to the IP address (e.g., 10.0.0.1) of the new host (i.e., the receiving host peer node) being used to replay the capture file. For example, suppose the host name of www.google.com, which may represented by a length of 14 bytes, is to be replaced with an IP address 10.0.0.1, which may have a length of 8 bytes during runtime. Thus, a differential (e.g., difference in payload length) of −6 bytes is introduced in the sequence number (or acknowledgment number) for all subsequent packets. Due to this sequence numbering discrepancy that is not accounted for by the transmitted/received packets, a receiving peer node or device under test (DUT) will not accept any subsequent packets thereby causing the replay to fail.
Similarly, additional discrepancies may be encountered when a DUT sequence number randomization feature is enabled in a DUT. With this feature activated, the DUT modifies the sequence number of any received SYN packet and maintains an internal sequencing/numbering value based on the modified value. Thus, if a sending or receiving peer node fails to account for this difference, the DUT will drop all received packets and the replay will fail.
Accordingly, a need exists for improved methods, systems, and computer readable media for updating sequence and acknowledgment numbers associated with replay packets.